1. Field of the Invention
The present invention relates to a quantum device using a quantum well layer.
2. Description of the Related Art
A semiconductor memory such as an electrically erasable and programmable read only memory (EEPROM) and a flash memory comprises a layer for accumulating electrons or holes surrounded by an insulator (such as a silicon dioxide film) placed between a substrate and a gate electrode of a metal oxide semiconductor (MOS) transistor. With an application of high voltage to the gate electrode and between source and drain electrodes of such a semiconductor memory, electrons or holes are conducted through the insulator by means of the tunnel effect. The electrons or holes are thereby accumulated in the accumulation layer. A difference in the number of electrons or holes is retained as a difference in data. The retained data is read through utilizing a fact that a current flowing between the source and drain electrodes changes in response to the number of electrons or holes accumulated in the accumulation layer.
A device for modulating a current, represented by a field effect transistor and a bipolar transistor, is capable of changing the magnitude of current flowing between the source and drain electrodes in accordance with a control voltage applied to the gate electrode.
However, the semiconductor memory and the device modulating a current described above each have the following problems. It is required to increase the thickness of the insulator of the semiconductor memory so that data is retained for an adequately long period. It is therefore required that a high voltage is applied to the gate electrode so as to perform writing and erasing of data within a practical span of time. It is thus difficult to achieve microstructuring of the device. The semiconductor memory further requires a feedback circuit for controlling the number of electrons or holes accumulated in the accumulation layer with a period in which a voltage is applied to the gate electrode. Consequently it takes a long time for writing and erasing of data and power consumption increases.
For the device modulating a current, a control voltage and a current are determined as a one-valued function. It is therefore required that a plurality of devices are coupled to each other with wiring for producing a function element such as a logic device. Such wiring increases floating resistance and floating capacitance so that high-speed operation is restricted. Power consumption and device size as a whole increase as well due to a plurality of devices coupled to each other.